This disclosure relates to cement spacer fluids for use in wellbores, methods for their manufacture, and methods of use.
Drilling fluids (or “muds”) used in the drilling of subterranean oil and gas wells and other drilling applications are well known. Drilling fluids carry cuttings and other particulates from beneath the bit, transport them through the annulus, and allow their separation at the surface while at the same time the rotary bit is cooled and cleaned. A drilling fluid is also intended to reduce friction between the drill string and the sides of the hole while maintaining the stability of uncased sections of the borehole. The drilling fluid is formulated to prevent unwanted influxes of formation fluids from permeable rocks penetrated. The drilling fluid may also be used to collect and interpret information available from drill cuttings, cores and electrical logs. It will be appreciated that as used herein, the term “drilling fluid” also encompasses “drill-in fluids” and “completion fluids”.
A spacer fluid, in contrast, is a liquid used to physically separate one special-purpose liquid from another during a drilling operation. A cement spacer fluid separates drilling fluid from cement during cementing operations in a well bore. Prior art cement spacer fluids are designed to be turbulent spacer fluids at low shear rates allowing them to displace viscous drilling mud from the wellbore. Some turbulent spacer fluids have certain drawbacks, for example, instability under operating conditions, especially at the higher temperatures as they can exist at the bottom of a wellbore. Others can allow mixing and remixing of the fluids they are designed to separate. In the case of separating drilling fluids from cement, such mixing and remixing results in reduced segregation performance, drilling mud contamination to the leading edge of the cement or cement slurry, limited capability to move drilling muds in the wellbore, low sweep efficiencies of water-based muds. Usually these disadvantages adversely affect the quality of the cementing operation in the drill hole, for example, by failing to adequately remove the drilling fluid the performance of the set cement slurry may be compromised with respect to its ability to bond to both the exposed rock surface in the drilled wellbore and to the tubulars placed in the wellbore.
Accordingly, there remains a need in the art for improved spacer fluids that overcome aforementioned drawbacks. In particular, a need remains for a cement spacer fluid that can effectively remove particulate such as drilling muds, as well as liquid contaminant particles.